Cancer is characterized primarily by an increase in the number of abnormal cells derived from a given normal tissue, invasion of adjacent tissues by these abnormal cells, or lymphatic or blood-borne spread of malignant cells to regional lymph nodes and to distant sites (metastasis). Clinical data and molecular biologic studies indicate that cancer is a multistep process that begins with minor preneoplastic changes, which may under certain conditions progress to neoplasia. The neoplastic lesion may evolve clonally and develop an increasing capacity for invasion, growth, metastasis, and heterogeneity, especially under conditions in which the neoplastic cells escape the host's immune surveillance (Roitt, I., Brostoff, J and Kale, D., Immunology, 17.1-17.12 (3rd ed., Mosby, St. Louis, Mo., 1993)).
Cancers figure among the leading causes of death worldwide, accounting for 8.2 million deaths in 2012. It is expected that annual cancer cases will rise from 14 million in 2012 to 22 million within the next two decades (See Cancer Fact sheet No 297, World Health Organization, February 2014, retrieved 10 Jun. 2014 and Globocan 2012, IARC).
The current drugs used in cancer treatment are highly toxic and often non-specific. Current anticancer therapy strategies are typically focused on rapid proliferating cells, which can shrink primary and metastatic tumors, but such effects are usually transient and tumor relapse of most metastatic cancers frequently occur. One possible reason for failure is the existence of cancer stem cells. Unlike most cells within the tumor, cancer stem cells are resistant to well-defined chemotherapy, and after treatment, they can regenerate all the cell types in the tumor through their stem cell-like behavior of largely quiescent nature and their abundant expression of drug transporters.
There is an enormous variety of cancers which are described in detail in the medical literature. The incidence of cancer continues to climb as the general population ages, as new cancers develop, and as susceptible populations (e.g., people infected with AIDS or excessively exposed to sunlight) grow. However, options for the treatment of cancer are limited. A tremendous demand therefore exists for new methods and compositions that can be used to treat patients with cancer.